CN1308274C - Production of 1, 2-dichloroethane - Google Patents

Abstract

The present invention relates to a method and apparatus for preparing 1,2-dichloroethane, which produces 1,2-dichloroethane by reacting ethylene with hydrogen chloride and an oxygen-containing gas to generate a reaction gas, the reaction being carried out in an oxychlorination reactor employing a fluidized bed, wherein at least one candle filter is used outside the oxychlorination reactor to filter the reaction gas.

Description

Preparation of 1,2-dichloroethane

technical field

The invention relates to a process and a plant for the preparation of 1,2-dichloroethane by the reaction of ethylene with hydrogen chloride and an oxygen-containing gas in an oxychlorination reactor with a fluidized bed for the formation of reaction gases .

Background technique

Oxychlorination can be understood as the reaction of olefins (here ethylene) with hydrogen chloride and oxygen or an oxygen-containing gas such as air and form saturated chlorinated alkanes (here 1,2-dichloroethane), which are given below Also referred to herein as "EDC". Here, the reaction proceeds according to the following equation:

.

However, the by-product water of this reaction can form very corrosive hydrochloric acid with the unreacted starting material hydrogen chloride, so that when carrying out these processes, it is necessary to use corresponding corrosion-resistant - and thus expensive - materials in a device for carrying out the method.

The oxychlorination reaction is carried out in the presence of a catalyst.

In one embodiment of the process, often applied on a large industrial scale, a catalyst fluidized bed is used as the catalyst in the oxychlorination reaction, the catalyst fluidized bed consisting essentially of copper chloride on an alumina support .

In this customary industrial fluidized-bed process, the catalyst is separated off in the upper part of the oxychlorination reactor by means of a plurality of cyclones connected one behind the other and thus largely remains in the reactor. Furthermore, here also a small portion of the catalyst, the so-called loss, gets into the reaction gas leaving the reactor and thus into the 1,2-dichloroethane refining process, where the catalyst has to be separated again.

From German laid-open patent document DE 41 32 030 a method is known for removing catalyst losses which occur in the reaction zone during the preparation of 1,2-dichloroethane according to the fluidized-bed oxychlorination process and which are combined with The crude EDC stream exits the reaction zone together. This removal takes place by separating the discharged catalyst losses from the crude EDC gas stream in a dry-running purification section. A preferred embodiment of this method has the following features: Catalyst losses are separated in a powder separator or electrofilter as purification zone, wherein the powder separator can be equipped with a bag filter which is purified with compressed circulating flowing gas . This makes it possible for catalyst losses separated in the purification zone to be desorbed and separated from the adsorbed reaction products in the subsequent desorption zone.

In such processes, it is to be avoided that waste water contaminated with heavy metals and inorganic deposits is formed when the water produced and the wash water used in the refining process is discharged. The disadvantage, however, is that the part of the catalyst that has been separated and no longer used must be discarded and properly disposed of. In addition, in this method, the problem of PCDD/PCDF (polychlorinated dibenzo-p-dioxin/furan) discharge into the environment from the waste water of the oxychlorination reaction is becoming more and more serious. It has also been found that this method is very expensive and has a high installation outlay, and thus leads to a high floor space and high investment costs.

DE-A-197 53 165 discloses a process for the preparation of 1,2-dichloroethane by oxychlorination in which ethylene is mixed with hydrogen chloride and an oxygen-containing Gas reaction, the reaction gas discharged from the reactor is finely filtered in the reactor to remove the catalyst, so that the catalyst remains in the reactor. The catalyst-depleted reaction gas is subsequently introduced into a quench tower and condensed in a known manner.

A disadvantage of this method is that fine particles accumulate in the reactor through filtration. This results in poor flow properties of the catalyst bed and poor heat transfer in the reactor. In addition, also because there is no pre-separation by the reactor cyclone, the particle content of the reaction gas is very high. Due to this high particle proportion, the filter area must be greatly enlarged. In addition, the method described in DE 197 53 165 can only be applied to existing installations with expensive installations, so that this method is only used on new installations and is almost unsuitable for existing installations.

It is also known from the prior art (Ullmann's Encyclopedia of Chemical Industry, Volume A6, 1986, page 269 (Ullmann's Encyclopedia of Industry Chemistry, Vol.A6, 1986, S.269)), from the oxychlorination fluidized bed The high-temperature reaction gas discharged from the reactor, which contains unconverted HCl gas in addition to the product 1,2-dichloroethane and water, is immediately quenched with an aqueous solution only. Here, catalyst losses that are not separated and hydrogen chloride that is not converted in the oxychlorination reaction are eluted from the ethylene. Not only external water but also water generated during the reaction, so-called reaction water, can be used as the washing liquid. EDC is distilled and condensed from the quench liquid along with water.

This method has proven to have the following disadvantages: The waste water resulting from the quenching has to be disposed of very expensively, since the waste water also contains catalyst losses.

All known prior art methods have the disadvantage that either only an insufficient PCDD/PCDF separation is possible, or that a sufficiently high separation rate can only be achieved with the aid of expensive equipment or by complex process steps.

Contents of the invention

It is therefore the object of the present invention to carry out the oxychlorination process for the preparation of 1,2-dichloroethane using a fluidized bed in such a way that catalyst losses formed during the reaction can be removed with as little effort as possible. Furthermore, the highest possible separation rate of catalyst loss should be achieved here.

A further object of the invention is to achieve a sufficient separation of PCDD/PCDF from reaction gases with as little equipment outlay as possible.

These objects are solved in a method of the type mentioned above in that the reaction gases are filtered outside the oxychlorination reactor with at least one candle filter.

Surprisingly, it has now been found that candle filters pose neither problems for ease of purification nor chemical durability (corrosion resistance) when filtering crude 1,2-dichloroethane gas streams under conventional conditions . This corrosion resistance was unexpected because the candle filter has a very large surface and corrosive gas mixtures of at least 200° C. flow through the candle filter.

According to a preferred embodiment of the present invention, the filter material used for the at least one candle filter is selected from the group consisting of at least one ceramic material, at least one sintered metal powder and at least one filter material made of refined steel (1.4571 or equivalent material) or wire mesh of one other suitable alloy such as a wrought steel alloy.

The filter material used for the at least one candle filter has an average pore size of 0.01-15 μm, preferably 0.1-8 μm, more preferably 0.2-5 μm and most preferably 0.8-3 μm.

For example, alloys are used in the at least one filter candle, such as the alloys known commercially under the names ®INCONEL, ®MONEL and/or ®HASTELLOY.

Candle-shaped filters of ceramic material with a corresponding average pore size can likewise be used.

When using such filter materials, PCDD/PCDF can be separated particularly well from reaction gases. The separation efficiency with respect to dioxins and furans is also surprising because the material transport of these compounds is very complex and has not been studied in depth. Especially when the candle filter, or the filter material used in the candle filter, has an average pore size or separation threshold of ≤15 μm, preferably ≤8 μm, particularly preferably ≤5 μm or ≤1 μm, the separation of PCDD/PCDF can be greatly improved improve. As a lower limit for the average pore diameter or separation threshold, values of 0.0001 μm, 0.001 μm, 0.01 μm, 0.1 μm and 0.5 μm are quite possible. The filter material can therefore have, for example, an average pore size of 0.0001 to ≦5 μm. In contrast to this, it is not possible to separate dioxins/furans if fabric filters, which have hitherto been regarded as equally effective, are used.

If the reaction gases are additionally condensed directly, that is to say without quench condensation, the residual amounts of small amounts of PCDD or PCDF that may still be present enter the organic phase almost quantitatively, and the waste water produced from the oxychlorination reaction is almost non-existent. contain these substances.

Because now with the simplest devices, high separation efficiencies especially for polychlorinated dibenzo-p-dioxins/furans (PCDD/PCDF) can be achieved by applying an external filter device with at least one candle filter , so it is possible to greatly reduce the levels of this compound in wastewater, which would otherwise have to undergo costly treatment.

The problem of fine particles being deposited in the filter and thus clogging the filter can be solved by the flow guidance of the gas in the filter as follows: the settling velocity of the small particles of the catalyst and the gas (cycle gas, 1, 2 - The flow velocity of dichloroethane and process water) produces a velocity vector greater than zero.

As mentioned above, it is possible for certain applications that the reaction gases be condensed directly after fine filtration without prior quenching, so that the method step of quenching, which was previously required in the prior art, can be dispensed with. The oxychlorination process can thus be made simpler and less expensive. In a method of this type, it is thus possible to use a device which does not have to have a so-called quench tower, which leads to a saving of space in the device used.

The process conditions, in particular the process conditions of the oxychlorination step with a fluidized bed, can preferably be carried out in conformity with the process conditions described in German patents 1 518 931 and 1 468 489, where the conditions are varied with reference to these publications The conditions described in this invention.

Preferably, in the process according to the invention, the reaction gas flows through the candle filter after leaving the oxychlorination reactor at a pressure of about 1-6 bar, preferably about 3.5 bar.

Here, the reaction gas should have a temperature of approximately 200-250° C., preferably approximately 220° C., when passing through the filter.

When the velocity vector produced by the sedimentation velocity of the small particles of the catalyst and the flow velocity of the gas (circulation gas, 1,2-dichloroethane and process water) obtained in the direction of gravity is greater than 0, especially greater than 10mm/sec, it can be used in Particularly good results were obtained in the method according to the invention.

After the reaction gas is filtered, it can be introduced into the quenching tower or directly condensed depending on the degree of purification.

In these methods, it is also possible to use a device of very simple construction, because the removal of catalyst loss does not have to be carried out by means of other expensive devices, such as by means of the expensive device described in DE 197 53 165 .

Preferably, the ratio of polychlorinated dibenzo-p-dioxin/furan (PCDD/PCDF) in 1,2-dichloroethane after the process according to the invention is less than 0.1 μg/ton , 2-dichloroethane.

The separation rate of the small catalyst particles entrained with the oxychlorination process using a fluidized bed is 99.99% in the process according to the invention according to a preferred embodiment.

Filtration with a candle filter for carrying out the process according to the invention and located outside the oxychlorination reactor, in the simplest way after the existing oxychlorination plant with fluidized bed This is also possible. This can therefore also be done particularly easily, since the filter used with at least one candle filter can be constructed very compactly.

Furthermore, due to the high operating reliability of the candle filter, it is also possible not to use backup devices.

Also since the candle filter has virtually no wear, it has an infinite life. At the same time, the filtered small particles can be easily removed when the gas flow passes through the candle filter according to the invention. This has also proven to be advantageous in that no expensive maintenance work has to be carried out.

In particular, in order to be able to carry out the process according to the invention particularly well, the plant for the preparation of 1,2-dichloroethane according to the oxychlorination process should have gas inlets for hydrogen chloride and oxygen, which are fed directly into the oxygen Fluidized bed of chlorination reactor. The inlet for hydrogen chloride and/or oxygen-containing gas is arranged directly in the fluidized bed of the fluidized bed reactor.

In this case, the inlet openings have a porous, gas-permeable profile.

It is also particularly advantageous if the ethylene and/or recycle gas stream enters the oxychlorination reactor through a bottom having a porous, gas-permeable material, which facilitates the formation of a fluidized bed. or have profiles made of porous, gas-permeable material. The arrangement of the input line can be selected, for example, in the type and manner described in DE 199 03 335, the arrangement described is adopted here with reference.

Further advantages and further developments of the invention emerge from the claims, the drawings and the following description, the invention being described in detail in an exemplary embodiment in relation to the drawings.

Description of drawings

Figure 1 illustrates an apparatus according to a preferred embodiment of the invention.

Detailed ways

The method according to the invention is also explained below with reference to the figures.

The preheated reactants hydrogen chloride and oxygen are directly introduced into the reaction chamber of the reactor 3 through the pipeline 1 . Simultaneously preheated cycle gas and ethylene are introduced into reactor 3 via another line 2 . The catalyst is in reactor 3, but not shown. The crude 1,2-dichloroethane stream, process water and recycle gas are directed via cyclone 4 to fine filter 6 . The separated catalyst fine powder is discharged from the system through the discharge port 7. Preheated backwash gas for cleaning (backwashing) of the filter components is conducted via a third line 5 into the filter 6 . The crude 1,2-dichloroethane stream freed from significant amounts of fines, process water and recycle gas is directed via another line 8 to a condenser 9 where the EDC and water vapor are condensed. The liquid EDC/water mixture is separated from the cycle gas in separator 10 and sent via line 12 to the refining step. The cycle gas is fed back again via line 11 to the suction side of the cycle gas compressor.

Example 1

An oxychlorination reactor with a fluidized bed was used to produce 1,2-dichloroethane, with _CuCl2 used as catalyst. Here, the oxychlorination reaction is carried out under common method conditions known to those skilled in the art, so no specific enumeration is given here.

Fine filtration of the reaction gases (500Nm ³ /h) after leaving the fluidized bed reactor from the purification zone in dry operation at a temperature of 200-250 °C (preferably 220 °C) and a pressure of about 1-6 bar (preferably 3.5 bar) The catalyst is passed through to separate the small particles of catalyst mixed together, the so-called catalyst loss, so that the catalyst is actually completely separated.

The fine filter consists of 8 filter parts. The filter parts are made of material 316S (stainless steel). The 8 filter elements are periodically backwashed through automatic valves. Preheated nitrogen was used as backwash gas, which had a pressure of 8 bar. The fine powder separated on the cone surface of the filter is removed once a day through the discharge port.

Here, the flow of the reaction gas is controlled such that the velocity vector resulting from the settling velocity of the small catalyst particles and the flow velocity of the gases (cycle gas, 1,2-dichloroethane and process water) in the direction of gravity is greater than 0 .

This ensures optimum deposition of fine particles.

Then, the reaction gas having a temperature of 200-250° C., preferably about 220° C. and having been depleted of catalyst, is led through a pipe to a condenser, where EDC and product water are condensed. In a gas separator, the condensed liquid is separated from the recycle gas. The EDC/water mixture is piped to a separation vessel where the aqueous phase is separated from the EDC.

The following concentrations of polychlorinated dibenzo-p-dioxins/furans were measured in oxychlorinated wastewater: no filter fabric filter Sintered metal filter (stainless steel), average pore size <5μm PCDD/PCDF TEQ according to NATO/CCMS (μg/ton OC capacity) 5 4.5 <0.1

Explanation of abbreviations:

PCDD = polychlorinated dibenzodioxins

PCDF = polychlorinated dibenzofurans

TEQ = toxic equivalent

NATO/CCMS=North Atlantic Treaty Organization/Committee on the Challenges of Modern Society

μg=microgram

tOC = tons of oxygen chloride capacity

This means that, according to the method of the present invention, the PCDD/PCDF content after filtration by a candle filter with a special average pore size is reduced by more than 97% compared with the PCDD/PCDF content after filtration by a fabric filter commonly used in the prior art.

Therefore, the separation rate of the accompanying small catalyst particles is greater than 99.99%. As a result, the content of polychlorinated dibenzo-p-dioxins/furans in the wastewater is greatly reduced. Consequently, a very costly and time-consuming disposal of the waste water produced after oxychlorination is not necessary.

Claims (22)

1. A process for preparing 1,2-dichloroethane, which produces 1,2-dichloroethane by reacting ethylene with hydrogen chloride and an oxygen-containing gas in an oxychlorination reactor to generate a reaction gas, wherein It is characterized in that at least one candle filter is used outside the oxychlorination reactor to filter the reaction gas. 2. The method according to claim 1, characterized in that the filter material used for the at least one candle filter is selected from the group consisting of: ceramic material, sintered metal powder and made of refined steel or refined steel alloy wire mesh. 3. The method according to claim 1 or 2, characterized in that the filter material used for the at least one candle filter has a mean pore size < 15 [mu]m. 4. The method according to claim 3, characterized in that the filter material has an average pore size ≤ 8 μm. 5. The method according to claim 3, characterized in that the filter material has an average pore size ≤ 5 μm. 6. Process according to claim 1 or 2, characterized in that the reaction gas is passed through the candle filter at a pressure of 1-6 bar. 7. Process according to claim 1 or 2, characterized in that the reaction gas at 200-250°C is passed through the candle filter. 8. The method according to claim 1 or 2, characterized in that the flow orientation of the gas in the candle filter is selected such that the flow velocity of the small particles to be filtered out and the settling velocity of the gas obtained in the direction of gravity The velocity vector is greater than 0. 9. A method according to claim 8, characterized in that said granules are catalyst granules. 10. A method according to claim 1 or 2, characterized in that the reaction gases are, after filtration, led to a quench tower or directly condensed. 11. Process according to claim 1 or 2, characterized in that the polychlorinated dibenzo-p-dioxin/furan ratio in the fluidized bed oxychlorination wastewater is less than 0.1 μg/ton 1,2 - dichloroethane. 12. Process according to claim 1 or 2, characterized in that the separation rate of the catalyst loss from the reaction gas is greater than 99.99%. 13. A plant for the preparation of 1,2-dichloroethane by reaction of ethylene with hydrogen chloride and an oxygen-containing gas in a process according to one of claims 1 to 12, having an oxychlorination reactor and a filter The device is characterized in that the filter has at least one candle filter arranged outside the oxychlorination reactor. 14. The device according to claim 13, characterized in that the at least one filter candle has a ceramic material, sintered metal powder, a wire mesh made of refined steel or a refined steel alloy. 15. Device according to claim 13 or 14, characterized in that the filter material used for said at least one candle filter is an alloy selected from the group consisting of ®INCONEL, ®MONEL and/or ®HASTELLOY. 16. The device according to claim 13, characterized in that the filter material used for said at least one candle filter has an average pore size of 0.01-15 [mu]m. 17. The device according to claim 16, characterized in that said filter material has an average pore size of 0.1-8 [mu]m. 18. The device according to claim 16, characterized in that said filter material has an average pore size of 0.2-5 [mu]m. 19. The device according to claim 16, characterized in that said filter material has an average pore size of 0.8-3 [mu]m. 20. Plant according to claim 13, characterized in that the inlet for hydrogen chloride and/or oxygen-containing gas is arranged directly in the fluidized bed of the fluidized bed reactor. 21. The device as claimed in claim 20, characterized in that the inlet has a porous, gas-permeable profile. 22. Apparatus according to claim 13, characterized in that the cycle gas and/or ethylene are fed into the oxychlorination reactor via a bottom having a porous, gas-permeable material.